This invention relates to a method for the direct reduction of metal oxides, ores, and the like to a highly metallized product which is discharged at high temperature and is particularly well suited for briquetting or other means of densification.
Cold discharge furnaces for the direct reduction of iron oxides to sponge iron have proven to be very successful commercally. However, merely omitting the cooling means for a direct reduction furnace is insufficient to achieve a satisfactory hot discharge furnace. In counterflow shaft type furnaces in general, and in shaft furnaces for direct reduction of iron in particular, the highest gas pressure in the furnace is always in the lower region of the furnace due to the upwardly flowing gases. In the direct reduction of iron, the gases in the furnace are highly flammable due to the high content of CO and H.sub.2 which are necessary for reduction of iron.
In shaft furnaces containing highly flammable gases, the furnace discharge region from which the processed solids are discharged is subject to the hazards of fire which can both harm personnel and damage equipment. This is particularly true where the solids are discharged hot for further processing such as the hot briquetting of direct reduced iron. Thus, the principal problem which must be overcome is that the furnace discharge outlet must be provided with means for preventing leakage of highly combustible gas. Also, the seal gas must not adversely affect the discharge temperature of the hot product. Mechanical valves or locks have been tried without success in hot discharge direct reduction furnaces. These mechanical devices tend to become bound or stuck because of the softness and stickiness of the hot reduced iron product. This usually causes such valves to leak.
In the present invention, a hot discharge shaft furnace for the direct reduction of iron is directly coupled to a hot briquetting machine for densifying the direct reduced iron product. Although the hot briquetting machine is directly coupled to the furnace discharge, it is isolated from the highly flammable gases which are maintained at relatively high pressure in the reduction furnace by a seal gas system at the lower end of the furnace. This seal gas system insures that the gases present at the furnace discharge are non-flammable despite the highly flammable character of the gases present within the reduction furnace.